The Global Amphibian Crisis

There’s a fungus that infects many kinds of amphibians. Some get wiped out entirely—but it’s harbored harmlessly by others, so it’s impossible to eradicate. Over a hundred species have disappeared in the last 20 years!

The fungus causes a disease called chytridiomycosis. The effects are gruesome: when spores land on a susceptible amphibian, they quickly sprout and form a vase-shaped structure that harvests energy from the animal’s skin. This produces more spores, which swim around using flagella and spread. The disease progresses as these reinfect the host. The victim may become lethargic, lose skin over its body, go into convulsions, and die.

Herpetologists and wildlife biologists began observing inexplicable disappearances of amphibians around the globe in the mid-1970s and especially by the mid-1980s but were at a complete loss to explain them. Finally, in the late 1990s, an insightful team of pathologists at the U.S. National Zoo, led by Don Nichols, collaborated with one of the few chytrid fungus scholars in the world, Joyce Longcore, and identified this quite unusual new genus and species.

Conservationists and disease ecologists were unprepared for the reality of a pathogen capable of directly and rapidly—mere months!—causing the elimination of a population or an entire species that was otherwise robust. Classical host-pathogen theory held that such dramatic consequences to the host population or species were only realized when the host population was already drastically reduced in size or otherwise compromised. The concept of a lightning extinction was foreign to researchers and conservationists, and we argued vehemently about it throughout the 1990s at symposia worldwide.

In retrospect, the scenario of a spreading pathogen is parsimonious and clear, but in the midst of the massacre we were entangled in logical quagmires along these lines: “The disappearances cannot be the result of disease; diseases are not capable of such.” Not to mention the fact that the smoking gun, the pathogen itself, was not described until 1999. While we were debating the issue, a terrible lesson was playing out for us around the world as an unknown disease decimated amphibian populations.

What are the ‘lessons’ that Mendelson is talking about? Here are some:

Our powerlessness in this terrible crisis must be balanced by increased efforts in realms that we can control, such as reducing carbon emissions to protect what habitat remains from chemical and physical disruption. We can go further and restore what has been wounded but can still be salvaged. We need to inspire and fund truly innovative research on pathogens in order to better predict and thwart emerging infectious diseases. The lessons we learn here will extend far beyond the amphibians. We must support funding for programs such as the Amphibian Ark and the Amphibian Survival Alliance. We must keep looking for species gone missing, and continue biodiversity surveys, despite the sometimes paralyzing depression that both activities can induce in this era. But especially, we need to pay close attention to the lessons that legions of dead amphibians are teaching us. I note with some satisfaction that our colleagues in bat research and conservation did not spend a decade arguing whether the fungus that causes white-nose syndrome could possibly eliminate entire colonies of bats in a single season. Our colleagues assumed that it was possible and reacted quickly. We can thank the amphibians for leaving us that lesson, but at such cost.

Yes, millions of bats in America have died from a new fungal disease called white-nose syndrome.

What role, if any, do people play in the spread of these new diseases? Why are they happening now?

In the case of amphibians, people helped spread American bullfrogs. These are resistant to the disease, but carry it. They’ve largely taken over here in Singapore.

Global warming seems not to be responsible, because the worst outbreaks happen at high elevations, where it’s cool: that’s where the fungus thrives.

As for the bats, the same fungus that’s killing bats in America is found in healthy bats in Europe, which suggests the disease spread from there. People might carry spores on their clothes from infected caves to not-yet-infected ones, so visitors to caves with bats are being asked to limit their activities, and disinfect clothing and equipment. It’s completely against the rules to visit some caves now.

There have been successful attempts to cure some amphibians of chytridiomycosis:

• Reid Harris of James Madison University has claims that coating frogs with Janthinobacterium lividum protects them from chytridiomycosis.

• A team of scientists published a paper claiming that Archey’s frog (Leiopelma archeyi), a critically endangered species in New Zealand, was successfully cured of chytridiomycosis by applying chloramphenicol topically.

• Don Nichols claims to have cured several species of frogs using a drug called itraconazole.

• Figure things out. Zoos don’t even know how to breed common toads without using artificial hormone injections! If you could find a way, maybe the same technique could be used with threatened species.

• If you’re a student, go to James Madison University and work with Reid Harris:

One should always be careful not to introduce foreign species in the wild. From Wikipedia :

The majority of these introductions were ill-advised; in most countries where mosquitofish have been introduced, endemic fish species were proven to already provide maximal mosquito control, and the introduction of mosquitofish has been both unnecessary and highly damaging to endemic fish and other endemic aquatic life. In Australia, G. holbrooki has caused great damage to indigenous fish and frog species. For example, it is considered responsible for the extinction of rainbowfish in subtropical streams around Brisbane.

However, in some areas, introduction of mosquitofish did help in eradicating malaria

[…] We studied the population genetics of chytridiomycosis using DNA sequences from a global panel of strains. These data showed evidence of a strong genetic bottleneck in the history of the pathogen, and the epidemic appears traceable to the widespread dispersal of a single genotype. Populations were not structured by host-origin, and the same lineage was detected in populations of both resistant and highly sensitive species. The data suggest that the chytridiomycosis epidemic is caused by the emergence of a novel pathogen but that disease outcome is contingent on host resistance and environmental factors. […]

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